Most ceiling fans are electrically powered. Typically they comprise an electric motor that is suspended beneath a ceiling by a hollow downrod through which electrical wires extend from building line power to the motor stator windings. An annular array of fan blades is mounted about the motor rotor by means of blade irons. As the rotor is rotatably mounted about the stator, rather than inside of it as conventional for electric motors, this type of motor is commonly referred to as an inside-out motor.
A problem common to such inside-out dynamoelectric motors is that of internal heating. High motor temperature operations adversely affect both motor operational efficiency and motor reliability and longevity. This problem is inherently more difficult to solve with inside-out electric motors since the stator and its windings, which become heated when energized, are both stationary and located inside surrounding structure, namely the rotor.
As shown in U.S. Pat. No. 5,883,449, this problem has heretofore been addressed by providing the rotor with an annular array of peripheral fins located about an internal impeller. The impeller serves to create low pressure on one side of the stator which, in combination with the peripheral fins, draws air from outside the motor casing across the stator windings and out of exhaust vents. Though this has provided stator cooling, the cooling has been limited by the internal location of the impeller. Also the fins inherently provide a structural mass that, though such does impel air, does so at the cost of restrictions in air flow and diminished returns in stator cooling. In part such is attributable to the fact that the fields of fins have been provided over both sides of the stator coils and have produced air turbulency. The addition of the impeller and fins also increased the cost of the motor.
Accordingly, it is seen that were an inside-out ceiling fan motor to be devised with simpler and more effective stator cooling means, both cooling and cost efficiency could be achieved. It thus is to the provision of such a ceiling fan motor that the present invention is primarily directed.